This invention relates to a transmission system, and particularly a system of transmitting data among plural semiconductor devices and a system of serially transmitting data on one line.
Conventionally, a three- or two-wire for serial data transmission system is usually used as a system for serial data transmission system. In the three-wire for serial data transmission system, two semiconductor devices, for example, one clock terminal and the other clock terminal of LSIs, a serial signal input and a serial signal output, and a serial signal output and a serial signal input are connected with each other, respectively, and one device supplies clock as a master, and the other device operates as a slave, wherein serial transmission is carried out with shifting data bit by bit according to number of pulses of clock. Further, when two devices mutually transfer data signal, it is necessary that data transmission is carried out, for example, by a system wherein two devices mutually output a busy signal for representing one's own status, and so four or five lines are used.
However, it is undesirable that some terminals of semiconductors such LSIs are occupied for serial data transmission, since other functions thereof are decreased. Further, in the case of bonding between chips in such a manner that the chips seemingly appear to be equal to one chip, in an application in which two semiconductors, for example LSIs are put in one package, it is preferable that the number of wire bondings between chips is as small as possible. When the number of wire bondings between chips are great, there is a problem on yield. Further, there is a problem that portions of bonding pads result in a primary factor by which on area of a chip is increased, thus cost being increased.